Influence of temperature and pH on the quality of metastable iron phases produced in zinc-rich solutions

The hydrolysis of ferric iron at elevated temperatures and pH values between 1.5 and 3.5 was characterized by determining the stability regions for schwertmannite, 6-line ferrihydrite and 2-line ferrihydrite, and linking them to the supersaturation levels present during their formation. It was shown that most industrial iron removal processes are operated above the metastability limit. However, stagewise precipitation of iron, even above the metastability limit, yielded better quality precipitates. Furthermore, careful selection and control of pH and temperature are required to improve product quality expressed in terms of the solids impurity content, dry solids density, particle size and the particle number density.